In U.S. Pat. Nos. 4,608,040; 4,776,833; 5,222,933; 5,421,806; 5,230,797 and 5,338,284 of Benjamin Knelson and now assigned to the present Assignee discloses a number of different arrangements of centrifugal separator of the type including a rotatable bowl having a peripheral wall of generally frusto-conical shape on which is provided a plurality of axially spaced, annular recesses. The particulate material containing fractions of different specific gravity to be separated is fed in slurry form through a feed duct to a position at or adjacent a base of the bowl so that the feed materials pass over the peripheral wall with heavier particulate materials collecting in the annular recesses while lighter particulate materials escape from the bowl through the open mouth. In the above patents, all of the annular recesses are fluidized by the injection of fluidizing water through holes in the peripheral wall at the respective recesses thus acting to fluidize the collecting material within the recesses.
A further arrangement is disclosed in U.S. Pat. No. 5,586,965, issued Dec. 24, 1996 of the above inventor in which the number of recesses is reduced and a frusto-conical lead-in section of the bowl is provided which is free from fluidized recesses so that the feed material is deposited onto the lead-in section and flows over that lead-in section prior to reaching the first annular recess.
In all cases the fluidized recesses are formed by providing drilled holes through the base of the recess in the manner disclosed in U.S. Pat. Nos. 4,608,040 and 5,230,797 above. This provides requirements on the construction and location of the holes which can lead to blockage and can limit the ability to tailor the arrangements to the best processing parameters.
In Australian Published Application 22,055/35 published 2 Apr. 1935 by Macnicol is disclosed a centrifuge bowl where the recesses on the peripheral wall are fluidized by injecting water through the wall and where the holes through the wall are covered by a band of screen material applied on the inside surface of the wall. The purpose of this screen is not explained. This device has not achieved commercial success and the disclosure has been long abandoned as a workable arrangement.
In Canadian Patent Application 2,085,064 of the above inventor published 12 Jun. 1993 is disclosed an arrangement using the machine having conventional V-shaped recesses of the type disclosed in the above patents in which an annular insert of a screen mesh material is placed in each recess at a position spaced from the base of the recess and spaced from the mouth of the recess with the intention of forming a recess which is shallower than the conventional recess. The shallow recesses are intended to form a concentrate which is richer than that of a conventional concentrator since less material is collected in each recess and it is stated that the machine is intended to be used as a “final separator” in a process of repeated concentration. Thus the inventor intended that in a line of conventional separators, the last would be modified from the conventional by the addition the mesh material inserts to form the special shallow recesses for the last separator only.
In Canadian Application 2,443,239 filed Oct. 15, 2003 by the present assignees and published on Dec. 28, 2003 which corresponds to U.S. Pat. No. 6,997,859 issued Feb. 14, 2006 is disclosed an arrangement of the above type in which an insert ring is provided which is inserted into at least some of the recesses to define a base of the recess with the ring being perforated and spaced from the bottom of the recess. The ring is thus a replaceable item within the bowl.
In Canadian Application 2,529,977 filed Dec. 6, 2005 by the present assignees and published on Jun. 22, 2006 which corresponds to U.S. Pat. No. 7,144,360 issued Dec. 5, 2006 is disclosed an arrangement of the above type in which some of the recesses are at least partly defined by a removable insert member arranged to be attached to a suitable mounting on the wall of the bowl. Each insert member includes a face portion defining a surface facing toward the axis of the bowl for engaging the slurry and preventing wear. The face portion may include a side portion on one side or both sides located radially inwardly of a rib on a respective side of the recess and at least partly covering the rib so as to prevent the slurry from contacting the rib and causing wear to the rib.
In U.S. Pat. No. 4,983,156 (Knelson) issued Jan. 8, 1991 is disclosed a centrifugal separator for extracting heavy metals from a slurry which comprises a centrifuge bowl having an inwardly facing surface over which the slurry runs. A dam at a discharge end of the surface forms a shallow layer of particles which separate preferentially the heavy metals. The surface includes a portion formed by a plurality of annular membrane portions spaced axially and separated by radial rings extending from the surface to a supporting metal bowl. The membranes are deflated or retracted to gradually form annular cups for receiving the separated metals. The membranes are then inflated to discharge the collected materials while the feed is temporarily halted and the bowl continues to rotate. A similar arrangement is shown in U.S. Pat. No. 2,179,807 (Asmussen) issued Nov. 14, 1939.